Improve handcrafted evaluation

[KnightStackSys]

Expands the handcrafted evaluation on top of current main while keeping search behavior unchanged.

4PC-oriented HCE terms

• bishop pair bonus
• supported pawn bonus, including support from the teammate's pawns
• team-aware king pawn shield
• penalty for a player currently in check
• king-zone pressure penalty based on adjacent king squares attacked by the opposing team
• partner coordination bonus for pieces directly defended by the teammate
• side-to-move tempo bonus

Existing terms preserved

• material
• mobility
• team-relative scoring

Removed generic assumptions

• removed pawn-advancement scoring because promotions are comparatively rare in 4PC
• removed knight-centralization scoring because the 14x14 cross-board geometry does not make centralization a consistently good knight heuristic

Tuning

All positional terms are exposed through the existing UCI tuning system so they can be adjusted without recompiling.

Scope

• include/ironphoenix/tuning.hpp
• src/eval.cpp
• src/tuning.cpp
• no search/pruning changes

This should be strength-tested directly against main before merge.